1. Field of the Invention
The present invention relates generally to altimeters, and, more particularly, to a device and method for registering and displaying the altitude of a location above sea level.
2. Description of the Related Art
The air pressure measurement or the altitude measurement in a corresponding, for example electronic, measuring device is carried out by means of a pressure measuring sensor. This sensor functions on a mechanical basis in that a diaphragm in the interior of the housing bends slightly when changes in pressure occur. This change is measured and conditioned in an electronically converted fashion. Each pressure measurement and the altitude measurement which is derived therefrom is made according to this mechanical principle.
An altimeter calculates the altitude on the basis of the air pressure. Here, the air pressure at sea level is assumed to be a zero point pressure. This zero point pressure is referred to as QNH. If therefore an air pressure is measured at a specific altitude, said air pressure is derived by means of a calibration curve, determined by average air pressures at respective altitude locations. On the basis of continuously changing air pressure under different weather conditions at the same location, it is possible to obtain differences in altitude measured values by derivation. This difference is approximately 8 m per 1 mbar change in pressure. Due to weather, the average air pressure of, for example at sea level, approximately 1,013 mbar fluctuates between 950 and 1,050 mbar. In other words, a measurement at sea level can yield fluctuations in altitude values of the order of magnitude of approximately 1,000 m.
Even on a calm day, fluctuations in air pressure due to temperature of +/xe2x88x921 mbar may occur. When there are rapid changes in the weather, for example cold fronts, the air pressure can change by up to 5 mbar within a day and the altitude deviation is thus approximately 40 m.
Due to these fluctuations in air pressure, an altimeter must be readjusted every time it is used if one wishes to have a correct display. This means that the altimeter must be reset at a known altitude, for example at home, in a railway station, a hut, etc., which is easy to forget. Altimeters are for this reason frequently no longer used because they are considered to be imprecise and unreliable as relatively large pressure fluctuations in the air pressure can lead to imprecise altitude values.
There is a need, therefore, for an improved device for registering and displaying altitude by measuring the ambient air pressure, and for an improved method for automatically correcting the altitude setting on a device for measuring the altitude above sea level by registering the ambient air pressure.
The present invention provides an altitude measuring device which provides better measuring accuracy and which is more user friendly.
According to the invention, an altitude measuring device is provided which permits automatic or semi-automatic setting of any one or more altitude values.